I would go with something like this. Highly rated, has a gauge to tell you when it is full of water and when it's full of water you plug it into a wall socket and overnight it dries it out. Many of the reviewers have put them into gun safes. http://www.amazon.com/Stack-On-SPAD-...productDetails

Also consider getting a humidity gauge for the inside of the gun safe, or if you want to spring for it one inside and one outside if you want to know how much drier it is inside vs ambient humidity in your house.

The heater types reduce relative humidity by warming the air, but mainly, by making the guns a little warmer than ambient, they prevent condensation when you remove them from the cabinet.

The desiccant types work until they are saturated. Generally, the amount of humidity in a closed space rises as their water content increases, so you want to "recharge" them (actually not charging, but driving water back out in a low oven). Or you can just get some of the smectite clay (bentonite or montmorillonite) type of granular oil absorbent or unscented and untreated kitty litter, spread it out on a cookie sheet and bake it for an hour at 450° or a little higher. While cooling, but still warm, drop it into an unwaxed plain brown paper bag, roll it up and put some rubber bands around it to keep it closed, and set it in the gun safe. This is what mil-spec desiccant is often made from. Moisture will permeate the paper bag just fine. This stuff has no color indicator, but a cheap humidity meter or dropping a small commercial silica gel pack with color indicator into the box with it will tell you when the humidity is no longer being controlled. Below about 40% R.H. rusting is essentially impossible, but below 60% it has a much harder time starting. Besides, below 50% you can get into issues with oiled wood getting too dry.

A compressor type dehumidifier is best if you have room for it. It draws water out of the air by condensation on a cooled coil, then puts it intp a collection container or runs it down a drain. Much more trouble than the other stuff as it needs not only AC power, but a drain tube or regular emptying. This is the fastest type for drying wet air.

Safe= large thermal mass. The reason it feels cold is the same reason it tends to make condensate out of normal house air. It's like the outside of your tea glass. The wet on the outside of your sweet tea came from the room.

I like the plug in and dry out type. There is no need to look for humidity in your safe, it's in the air already as a gas and will condense on metal surfaces in your safe. Making safes out of less conductive material would be the only solution I can think of.

Safe= large thermal mass. The reason it feels cold is the same reason it tends to make condensate out of normal house air. It's like the outside of your tea glass. The wet on the outside of your sweet tea came from the room.

You left out that the glass has to be colder than the ambient air temperature for that to happen. Same with the safe. It's the air at the chilled surface being cooled below its dew point (>100% RH) that causes it to be unable to keep all the water vapor in it dissolved. This is why the Goldenrod type heaters work.

Itar,

If you put the dehumidifier actually into the safe, it won't take long to get the bulk of the water out of the air and that won't be enough to fill the reservoir. But its humidistat will keep cycling it back on every time enough of that water re-evaporates from the reservoir or enough addition moisture dissolves in from the outside through anyplace in the safe that's not hermetically sealed. Similarly, if the air outside the safe is kept dehumidified, moisture in the safe will gradually work its way out.

You may find it less expensive (and less room consuming in the safe) to run one of the heaters inside it, but dehumidify the surrounding air as much as it is in your budget to do.

You left out that the glass has to be colder than the ambient air temperature for that to happen. Same with the safe. It's the air at the chilled surface being cooled below its dew point (>100% RH) that causes it to be unable to keep all the water vapor in it dissolved. This is why the Goldenrod type heaters work.

The crystal kitty litter is Silica Gel, same as the desiccant packs. The clay based ones are bentonite....and bentonite is a great desiccant, used in "desi-paks", among others. You can't go wrong with cat litter...no matter what anyone says.

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